7. The truth that Saunière wants to tell Sophie about her family haunts Sophie throughout the novel and eventually means more than Saunière consciously intended. Eventually, it is revealed that her family was not all killed in the car accident, that her grandfather was Grand Master of the Priory of Sion, and that she is of Merovingian descent (descended from the marriage of Jesus and Mary Magdalene). (Chapter 16, and throughout, especially Chapter 105)

8. A Christian building built on the ruins of an Egyptian temple to the goddess Isis, the Church of Saint-Sulpice represents how Christian history and doctrine is built on pagan roots. (Chapter 19)

9. The Rose Line is a brass strip that is a gnomen—a pre-Christian astronomical device similar to a sundial. It cuts the church in half, ending at an obelisk, and guides Silas to the false keystone. (Chapter 22)

10. The Priory of Sion (in French, the Prieuré de Sion) is a secret society with pagan roots, devoted to safeguarding the secret of the Holy Grail.
(Chapter 23)

11. When he broke the stone panel open, Silas found a reference to Job 38:11 on the false keystone, which reads, "Hitherto shalt though come, but no further." This indicates that he should be stopped here, by the false keystone, but using Job to do so also symbolizes the need to be sustained by faith in one's time of trials. (Chapter 29)

12. Aringarosa meets with Vatican representatives at Castel Gandolfo, the Pope's summer home. It is a more private place to meet than the Vatican, but it is also the site of the Specula Vaticana (the Vatican Observatory). This represents the attempt to bring science and religion together—and it is personally hateful to Bishop Aringarosa due to the nature of his faith. (Chapter 34)

13. On a practical level, Sophie and Langdon go through the Bois de Boulogne to get to the bank at 24 Rue Haxo. On a symbolic level, they go through the Bois de Boulogne to pass through a kind of symbolic test: a land of disordered sexual desire, where they must remain pure. (Chapter 37)

14. A cryptex is a coded cylinder built according to designs found in Da Vinci's diaries. It has several disks with letters on it that can be turned to spell out a code word. If someone tries to open a cyptex without the code, he or she would destroy the message hidden inside. (Chapter 47)

15. He must prove his identity to Sir Leigh Teabing as a "test of honor." Symbolically, this is a ritual test the Grail knight must pass to prove he is worthy to continue on the quest. (Chapter 52)

16. He walks her through an analysis of Da Vinci's painting The Last Supper, showing that each person had a cup, so the Grail could not be a cup. He then shows that the figure at Jesus's right is female. He also summarizes the history and legends surrounding the Grail. (Chapters 58 & 60)

17. Because it is symbolically appropriate: the end of the two thousand year period of the age of Pisces is ending, and the age of Aquarius beginning. (Chapter 62)

18. To incapacitate him, since he's holding a gun on Teabing, Sophie, and Langdon. He says he knows to hit him there because of the blood stain on his thigh from wearing the cilice, but he also knows Silas wears the belt because he is the Teacher. (Chapter 65)

19. Because her father showed her Da Vinci's mirror script when she was a child. (Chapter 71)

20. Because it requires special private knowledge passed on through direct oral transmission rather than public written knowledge, because reading it requires the reader to reverse their existing perspective on the world, and because Da Vinci's symbolic orders are central to this quest. (Chapter 72)

21. Heiros Gamos means "sacred marriage" in Greek. It refers to a sexual ritual in which men try to gain direct experience of the divine through sexual contact with women. It represents the need to unify the masculine and feminine in the world, and Sophie's accidental encounter with it when younger caused her break with her grandfather. (Chapter 74)

22. A bug was planted in the sculpture of a medieval knight on his desk. (Chapter 90)

23. Alexander Pope, the poet. (Chapter 95)

24. The Vatican decided to break off its formal relationship with the Opus Dei order at that time. (Chapter 100)

25. They go to Florence. They go there because Langdon has a conference there, because a romantic connection developed between them, and because the name of the city, Florence, contains the word "flor," referring to flowers, a symbol of the feminine—and because "Florence" means flowering, as their love is. (Chapter 105)

26. It is the original meridian, the zero longitude of the world; it splits the world in two as the Rose Line at Church of Saint-Sulpice splits the church. (Epilogue)